Conductive graphene-metal composite material, the production method of the same and use of the same

ABSTRACT

The invention provides a conductive graphene-metal composite material, which is a composite of monolayer graphene nanoflakes and metal or metal oxide. The monolayer graphene nanoflakes of the invention are made by exfoliating graphite, and have a good combination with metal material by adopting an ultrasonic treatment or a mechanical agitation treatment. The graphene is uniformly dispersed therein and forms a conductive network, which can improve the electrochemical activity efficiently and reduce the resistance against the transfer of the charges efficiently. Use of the graphene-metal composite electrode reduces the costs of processes and facilities, on the premise of good properties. It can be used to replace the ITO conductive layer of the liquid crystal display.

TECHNICAL FIELD

The invention relates to a conductive graphene material, specifically,to a conductive graphene-metal composite material, the production methodof the same and the use of the same.

BACKGROUND

Nowadays, the primary raw material for the transparent conductive layerof the array substrate and the colorfilm substrate in the production ofliquid crystal displays is indiumtin oxide (ITO), which is a metaloxide. ITO can provide high optical transparency and relatively goodconductivity. However, it exhibitsconductivity lower than metals such asgold and silver. Thus, there are some limitations when it is used in thefields of touch screens, displays, plasma displays, etc.

Additionally, the abrasion resistance of the ITO film is relativelypoor, and at the same time the cost of indium, which is the maincomponent of ITO, is relative high, therefore, the use of optical filmhaving better properties, such as graphene-metal composite electrode,has become a trend.

The monolayer graphene is a two-dimensional structure of a closelypacked atomic monolayer. The specific electronic configuration thereofdetermines its excellent electrical property. In the monolayer graphene,carbon atoms periodically arrange in the graphite plane in the form ofsix-membered ring. Each carbon atom binds three adjacent carbon atomsvia 6 bonds. The threehybridization orbitals, i.e. S, Px and Py, form ansp2 hybrid orbital, which imparts the graphene extremely high mechanicalproperties. The remainingπ electrons in the Pz orbital form a π orbitalin the direction perpendicular to the plane. The π electrons can move inthe plane of the graphene crystal, which allows the graphene to possessa good conductivity. Furthermore, investigations indicate thattransparency of a graphene electrode would not be affected when itcombines in a grid style with metal having small size.

Therefore, it is possible to develop a new alternative conductivematerial for indium tin oxide (ITO) for the production of the conductivelayer used in liquid crystal displays, by utilizing the superiorconductivity and transparency of the graphene.

SUMMARY OF THE INVENTION

An object of the invention is to overcome the disadvantages mentionedabove, that is, to provide a conductive graphene-metal compositematerial with low price, good conductivity and superior transparency.

Another object of the invention is to provide a production process ofsaid conductive graphene-metal composite material.

A further object of the invention is to provide said conductivegraphene-metal composite material in use for manufacturing a conductivelayer of a liquid crystal display.

In order to achieve the objects of the invention, the invention providesa conductive material, which is a composite of monolayer graphenenanoflakes and metal or metal oxide.

The conductive material can be used as an electrode material.

Here, aluminium is preferably adopted as the metal, and aluminium oxideis preferably adopted as the metal oxide.

The weight ratio between the monolayer graphene nanoflakes and the metalor the metal oxide is 1:50-1:600, preferably 1:100-1:400.

The monolayer graphene nanoflakes are prepared from graphite oxidepreferably by a rapid thermal exfoliation method or a solvothermalmethod, preferably by a rapid thermal exfoliation method.

The conductive material is prepared by subjecting monolayer graphenenanoflakes and a metal or metal oxide to phase coating and mixing,preferably by an ultrasonic treatment or a mechanical agitationtreatment to form a composite of monolayer graphene nanoflakes and ametal or metal oxide.

The invention provides a production process of a conductive material,characterized by including the steps of:

1) processing graphite oxide into a graphene suspension comprisingmonolayer graphene nanoflakes; and

2) processing the graphene suspension and metal or metal oxide so as toprovide a liquid comprising a composite as the conductive material.

Preferable, the step of processing the graphite oxide into a graphenesuspension comprising monolayer graphene nanoflakes may includeprocessing the graphite oxide into a graphene suspension comprisingmonolayer graphene nanoflakes by utilizing a rapid thermal exfoliationmethod or a solvothermal method.

Preferable, the step of processing the graphite oxide into a graphenesuspension comprising monolayer graphene nanoflakes may include:

subjecting the graphite oxide to a heat treatment;

adding absolute ethanol into the treated graphite oxide; and

subjecting the treated graphite oxide with absolute ethanol addedtherein to an ultrasonic treatment or a mechanical agitation treatment.

Preferable, the subjecting the graphite oxide to a heat treatment mayinclude heat treating the graphite oxide at a temperature of 850-1300°C. for 30-50 sec.

The step of processing the graphite oxide into a graphene suspensioncomprising monolayer graphene nanoflakes may includes:

subjecting the graphite oxide to a heat treatment;

adding absolute ethanol into the treated graphite oxide; and

subjecting the graphite oxide with absolute ethanol added therein to anultrasonic treatment, wherein the power of the ultrasound is 80-150 Wand the time of the ultrasonic treatment is 2-2.5 h.

Preferable, the weight ratio of the graphite oxide to the absoluteethanol may be 1:20-1:100.

Preferable, the step of processing the graphene suspension and metal ormetal oxide so as to provide a liquid comprising a composite mayinclude: subjecting the graphene suspension and metal or metal oxide toan ultrasonic treatment or a mechanical agitation treatment so as toprovide a liquid comprising a composite.

Preferable, the step of processing the graphene suspension and metal ormetal oxide so as to provide a liquid comprising a composite mayinclude:

mixing the graphene suspension and a solvent, so as to provide amixture;

subjecting the mixture to ultrasonic dispersion, so as to provide aultrasonically dispersed mixture; and mixing the ultrasonicallydispersed mixture and a salt solution comprising the metal andperforming an agitation treatment on it, so as to provide the liquidcomprising a composite.

Preferable, the solvent may be N-methyl-2-pyrrolidone.

Preferable, the ultrasonic dispersion may include dispersion of 20-60min under an ultrasound of 80-150 W.

Preferable, the salt solution comprising the metal may be a solutioncomprising Al³⁺ and SO₄ ²⁻.

Preferable, the duration of the agitation treatment may last 5-10 h.

Preferable, the weight ratio of the graphene in the graphene suspensionto the metal in the salt solution comprising the metal may be1:50-1:600.

Specifically, the production process of a conductive graphene-metalcomposite material of the invention includes the steps of:

1) processing graphite oxide into a graphene suspension comprisingmonolayer graphene nanoflakes by a rapid thermal exfoliation method or asolvothermal method; and

2) compounding the graphene suspension comprising monolayer graphenenanoflakes and metal so as to provide a composite by an ultrasonictreatment or a mechanical agitation treatment;

3) finally, treating it at high temperature, so as to provide theconductive graphene-metal composite material.

Said ultrasonic treatment or a mechanical agitation treatment includes:

a) mixing the graphene suspension and a solvent, so as to provide amixture;

b) subjecting the mixture to ultrasonic dispersion, so as to provide aultrasonically dispersed mixture; and

c) mixing the ultrasonically dispersed mixture and a salt solutioncomprising the metal and stirring it, so as to provide the liquidcomprising a composite.

Specifically, the rapid thermal exfoliation method in the step 1) is:firstly, heat treating the graphite oxide at a temperature of 850-1300°C. for 30-50 sec;subsequently, adding absolute ethanol therein; then,treating it under an ultrasound of 80-150 W for 2-2.5 h, so as toprovide a graphene suspension comprising monolayer graphene nanoflakes,wherein the weight ratio of the graphite oxide to the absolute ethanolis 1:20-1:100.

The ultrasonic treatment in the step 2) is: adding the graphenesuspension into a solution of N-methyl-2-pyrrolidone, dispersing itunder an ultrasound of 80-150 W for 20-60 min, adding a mixed solutioncomprising Al³⁺ and 50₄ ²⁻, and stiffing it for 5-10 h. In other words,in the ultrasonic treatment or the mechanical agitation treatment step2), the solvent is N-methyl-2-pyrrolidone. The ultrasonic dispersionincludes a dispersion of 20-60 min under an ultrasound of 80-150 W, thesalt solution comprising the metal is a solution comprising Al³⁺ and 50₄²⁻, and the stiffing lasts 5-10 h.

Here, the weight ratio of the graphene in the graphene suspension to thealuminium in the salt solution comprising Al³⁺ and 50₄ ²⁻ is 1:50-1:600,preferably 1:100-1:400.

The high temperature treatment in the step 3) removes the solvent in thecomposite, and ultimately makes the monolayer graphene nanoflakes andthe metal or metal oxideform a conductive network.

The invention adopts an ultrasonic treatment or a mechanical agitationtreatment. This can ensurea good combination between the metal materialand graphite active substance; and the method of mechanical agitationcan avoid that the graphene disperses non-uniformly and that it is hardto form a conductive network. This can improve the electrochemicalactivity efficiently and reduce the resistance against the transfer ofthe charges efficiently.

The conductive graphene-metal composite material can be used as aconductive electrode used in a transparent conductive layer of a liquidcrystal display, for example, a pixel electrode of an array substrate,and an electrostatic shielding layer in a color film substrate.

When a conductive layer is produced by using the graphene-metalcomposite material of the invention, following process can be used:

1) coating the graphene-metal compositeon an array substrate or a lowersubstrate in a FFS mode, wherein all other layers have been prepared onthe substrate previously; and

2) then treating it at high temperature under protection of an inertgas, so as to provide the conductive layer.

During the production, the substrate must be cleaned previously, by suchas washing it with an agent, rinsing it with water directly, drying itwith air knife, etc.

In step 1), the graphene-metal composite is spin coated on the substrateby a dipping process.

In step 2), the temperature of the high temperature treatment is100-250° C.

The substrate of the liquid crystal display of the invention comprises atransparent conductive layer, which is formed of the conductive materialmentioned above.

The liquid crystal display of the invention comprises a substrate, whichcomprises a transparent conductive layer, which is composed of theconductive material mentioned above.

The graphene-metal composite conductive material of the invention hasthe following advantages.

1. Themonolayer graphene nanoflakes adopted have a high conductivity anda large aspect ratio. The use of ultrasonic treatment and/or themechanical agitation treatment can ensure a good combination between themetal material and graphite active substance. And the method ofmechanical agitation can avoid that the graphene disperses non-uniformlyand that it is hard to form a conductive network. This can improve theelectrochemical activity efficiently and reduce the resistance againstthe transfer of the charges efficiently.

2. Because the nature of the material and the production process thereofare excellent, monolayer graphene nanoflakes have a character that it ismore transparent.

By the network formed by compounding it with the metal material, theelectron conductivity of the monolayer graphene nanoflakesis muchhigher.

3. When being compounded with metal, the transparency of the conductivematerial would not be affected due to that the metal exists in a nanostate.

4. On the premise of that the graphene-metal composite electrode of theinvention has good properties, the cost of the current process forsputtering ITO with a sputter can be reduced, and the costs of theprocesses and facilities can be reduced, therefore, this material can beused for replacing the ITO conductive layer of the liquid crystaldisplay.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow chart of the production process of the graphene-metalcomposite electrode of the invention.

EMBODIMENTS

The Examples below are provided to illustrate the invention, but notlimit the scope of the invention.

The conductive graphene-metal composite material of the invention is acomposite of monolayer graphene nanoflakes and metal or metal oxide. Themetal or metal oxide can be aluminium and aluminium oxide, respectively.As the metal, a metal that is appropriate in terms of conductivity andprice or cost, preferably aluminium, can be adopted. Other metal alsocan be used, such as Ag.

The conductive material is prepared by subjecting monolayer graphenenanoflakes and a metal or metal oxide to a phase coating and mixing byan ultrasonic treatment or a mechanical agitation treatment.

The weight ratio between the monolayer graphene nanoflakes and aluminiumor aluminium oxide is 1:50-1:600, preferably 1:100-1:400.

The monolayer graphene nanoflakes are prepared from graphite oxide by arapid thermal exfoliation method or a solvothermal method, preferably bya rapid thermal exfoliation method. Monolayer graphene nanoflakes thusobtained have high conductivity and large aspect ratio.

The production process of the conductive graphene-metal compositematerial of the invention includes steps of:

1) processing graphite oxide into a graphene suspension comprisingmonolayer graphene nanoflakes by a rapid thermal exfoliation method;

specifically, firstly heat treating the graphite oxide at a temperatureof 850-1300° C. for 30-50 sec, subsequently adding absolute ethanoltherein, then treating it under an ultrasonic wave of 80-150 W for 2-2.5h, so as to provide a graphene suspension comprising monolayer graphenenanoflakes, wherein the weight ratio of the graphite oxide to theabsolute ethanol is 1:20-1:100;

2) compounding the graphene suspension comprising monolayer graphenenanoflakes and metal or metal oxide material so as to provide acomposite by an ultrasonic wave treatment or a mechanical agitationtreatment;

specifically, adding the graphene suspension into a solution ofN-methyl-2-pyrrolidone, dispersing it under an ultrasonic wave of 80-150W for 20-60 min, adding a mixed solution (the solution can be a saltsolution or alkali solution comprising the metal) comprising Al³⁺ andSO₄ ²⁻, and stirring it under a rate of the agitation of 500-1000 rpmfor 5-10 h, wherein it is desired that the amount of theN-methyl-2-pyrrolidone added ensures the good dispersion of thegraphene, and preferably the volume ratio of the graphene suspension tothe solution of N-methyl-2-pyrrolidone is 1:1-1:5;

The weight ratio of the graphene in the graphene suspension to thealuminium in the mixed solution is 1:50-1:600;

The rate of the agitation is 500-1000 rpm; and

3) finally, by means of high temperature treatment, removing the solventin the composite and ultimately making the monolayer graphene nanoflakesand the metal or metal oxide form a conductive network useful in aconductive layer, wherein the temperature of the high temperaturetreatment is 100-350° C.

The conductive graphene-metal composite material of the invention can beused as a conductive electrode used in a transparent conductive layer ofa liquid crystal display, for example, a pixel electrode of an arraysubstrate, and an electrostatic shielding layer in a color filmsubstrate.

An embodiment of the present invention further provides a liquid crystaldisplay device comprising a conductive film, wherein the conductive filmis formed of the conductive material according to any embodiment of theinvention.

Example 1

As shown in FIG. 1, a flow chart of the production process of thegraphene-metal composite electrode of the invention is provided. Theproduction process of the graphene-metal composite electrode was asfollowings.

1) 50 g graphene oxide was taken and heat treated, wherein a rapid heatexpansion thereof over 30 sec in a muffle furnace at 1000° C. providedexfoliatable graphite. The resulting exfoliatable graphite was addedinto 5 L absolute ethanol (density: 0.79, with respect to water). Themixture was treated under an ultrasound of 100 W for 2 h to provide agraphene suspension (comprising monolayer graphene nanoflakes). 2) Theabove-mentioned graphene suspension was added into a 5 L

N-methyl-2-pyrrolidone, and then dispersed for 30 min by being placed inan ultrasonic cleaner at 100 W. 15 L mixed solution comprising Al³⁺ andSO₄ ²⁻ (concentration: 10 mol/L) was added therein. The mixture wasmagnetically stirred (stirring rate: 500 rpm) for 5 h to provide agraphene-metal composite.

3) The glass substrate was cleaned by rinsing it directly with water.Under the back side of the glass substrate of the array substrate inwhich all other layers had been prepared on the substrate previously,the graphene-metal composite was plated on the surface of the glasssubstrate by a dipping process.

4) The graphene-metal composite electrode (a composite of monolayergraphene nanoflakes and aluminium oxide, weight ratio: 1:160) wasproduced on the glass substrate by a high temperature treatment at 300°C. under the protection of an inert gas. It could serve as analternative electrode of the indium tin oxide (ITO) conductive layer,i.e. graphene-metallic aluminium composite electrode.

The graphene-metal composite electrode had improved transparency andconductivity. On the premise of good properties, the costs of processesand facilities were reduced.

Example 2

1) 100 g graphene oxide was taken and heat treated, wherein a rapid heatexpansion thereof over 50 sec in a muffle furnace at 1300° C. providedexfoliatable graphite. The resulting exfoliatable graphite was addedinto 5 L absolute ethanol. The mixture was treated under an ultrasoundof 120 W for 2.5 h to provide a graphene suspension.

2) The graphene suspension was added into an 8 L N-methyl-2-pyrrolidone,and then dispersed for 40 min by being placed in an ultrasonic cleanerat 150 W. 30 L mixed solution comprising Al³⁺ and 50₄ ²⁻ (concentration:5 mol/L) was added therein. The mixture was magnetically stirred (600rpm) for 8 h to provide a composite.

3) The glass substrate was cleaned by rinsing it directly with water.Under the back side of the lower glass substrate in the FFS mode, inwhich all other layers had been prepared on the substrate previously,the graphene-metal composite was plated on the glass substrate by adipping process.

The remaining steps were same as those in Example 1. Thereby agraphene-metal composite electrode (a composite of monolayer graphenenanoflakes and aluminium oxide, weight ratio: 1:81) was produced.

Example 3

1) 50 g graphene oxide was taken and heat treated, wherein a rapid heatexpansion thereof over 50 sec in a muffle furnace at 850° C. providedexfoliatable graphite. The resulting exfoliatable graphite was addedinto 2 L absolute ethanol. The mixture was treated under an ultrasoundof 80 W for 2.5 h to provide a graphene suspension.

2) The graphene suspension was added into an 8 L N-methyl-2-pyrrolidone,and then dispersed for 60 min by being placed in an ultrasonic cleanerat 80 W. 15 L mixed solution comprising Al³⁺ and SO₄ ²⁻ (concentration:20 mol/L) was added therein. The mixture was magnetically stirred (800rpm) for 8 h to provide a composite.

3) The glass substrate was cleaned by rinsing it directly with water.Under the back side of the lower glass substrate in the FFS mode, inwhich all other layers had been prepared on the substrate previously,the graphene-metal composite was plated on the glass substrate by adipping process.

The remaining steps were same as those in Example 1. Thereby agraphene-metal composite electrode (a composite of monolayer graphenenanoflakes and aluminium oxide, weight ratio: 1:324) was produced.

Test Example

The resistances of the transparent conductive layer thin films formed ofthe graphene-metal composite material of the invention were tested. Thecomparison between the results of them and an ITO thin film was shown inthe table below.

Surface Thickness d Resistance Transmittance [Å] Rs [Ω/□] (550 nm)Method of Measurement K-mac 4-Probe SU Optical Tester Tester Indium TinOxide (ITO) 400 60 ± 15 93% Thin Film Example 1 400 50 ± 15 95% Example2 600 60 ± 15 94% Example 3 1000 20 ± 15 93%

From this it could be seen, that compared with ITO thin film, thetransparent conductive thin films obtained in the present invention hadexcellent conductivity and transparency.

Although the invention is described above in detail by a generaldescription and specific embodiments, those skilled in the art willappreciate that it is obvious to them that different changes ormodifications can be made without departing the spirit and the principleof the invention. Therefore, all of such changes or modifications shouldbe involved in the extent defined by the claims of the invention.

What is claimed is:
 1. A conductive material, which is a composite ofmonolayer graphene nanoflakes; and metal or metal oxide.
 2. Theconductive material according to claim 1, wherein the metal and themetal oxide are aluminium and aluminium oxide, respectively.
 3. Theconductive material according to claim 1, wherein the weight ratiobetween the monolayer graphene nanoflakes and the metal or the metaloxide is 1:50-1:600.
 4. The conductive material according to claim 3,wherein the weight ratio between the monolayer graphene nanoflakes andthe metal or the metal oxide is 1:100-1:400.
 5. The conductive materialaccording to claim 1, wherein the monolayer graphene nanoflakes areprepared from graphite oxide by a rapid thermal exfoliation method or asolvothermal method.
 6. The conductive material according to claim 1,wherein the conductive material is prepared by subjecting monolayergraphene nanoflakes and a metal or metal oxide to a phase coating andmixing by an ultrasonic treatment or a mechanical agitation treatment.7. A method of producing a conductive material, the methodcomprising: 1) processing graphite oxide into a graphene suspensioncomprising monolayer graphene nanoflakes; and 2) processing the graphenesuspension and metal or metal oxide so as to provide a solutioncomprising composite, wherein the composite is the conductive material.8. The method according to claim 7, wherein the step of processing thegraphite oxide into a graphene suspension comprising monolayer graphenenanoflakes, comprising: processing the graphite oxide into a graphenesuspension comprising monolayer graphene nanoflakes by utilizing a rapidthermal exfoliation method or a solvothermal method.
 9. The methodaccording to claim 7, wherein the step of processing the graphite oxideinto a graphene suspension comprising monolayer graphene nanoflakescomprising: subjecting the graphite oxide to a heat treatment; addingabsolute ethanol into the treated graphite oxide; and subjecting thetreated graphite oxide with absolute ethanol added therein to anultrasonic treatment or a mechanical agitation treatment.
 10. The methodaccording to claim 9, wherein the subjecting the graphite oxide to aheat treatment, comprising: heat treating the graphite oxide at atemperature of 850-1300° C. for 30-50 sec.
 11. The method according toclaim 7, wherein the step of processing the graphite oxide into agraphene suspension comprising monolayer graphene nanoflakes,comprising: subjecting the graphite oxide to a heat treatment; addingabsolute ethanol into the treated graphite oxide; and subjecting thegraphite oxide with absolute ethanol added therein to an ultrasonictreatment, wherein the power of the ultrasonic wave is 80-150 W and thetime of the ultrasonic wave treatment is 2-2.5 h.
 12. The methodaccording to claim 9, wherein the weight ratio of the graphite oxide tothe absolute ethanol is 1:20-1:100.
 13. The method according to claim 7,wherein the step of processing the graphene suspension and metal ormetal oxide so as to provide a solution comprising composite,comprising: subjecting the graphene suspension and metal or metal oxideto an ultrasonic wave treatment or a mechanical agitation treatment soas to provide a solution comprising the composite.
 14. The methodaccording to claim 7, wherein the step of processing the graphenesuspension and metal or metal oxide so as to provide a solutioncomprising composite, comprising: mixing the graphene suspension and asolvent, so as to provide a mixture; subjecting the mixture toultrasonic wave dispersion, so as to provide a ultrasonically dispersedmixture; and mixing the ultrasonically dispersed mixture and a saltsolution or alkali solution comprising the metal, and then performing amechanical agitation treatment on it, so as to provide the solutioncomprising the composite.
 15. The method according to claim 14, whereinthe solvent is N-methyl-2-pyrrolidone.
 16. The method according to claim14, wherein the ultrasonic wave dispersion includes dispersion of 20-60min under an ultrasonic wave of 80-150 W.
 17. The method according toclaim 14, wherein the salt solution or alkali solution is a solutioncomprising Al³⁺ and SO₄ ²⁻.
 18. The method according to claim 14,wherein the duration of the mechanicalagitation treatment lasts 5-10 h.19. The method according to claim 14, wherein the weight ratio of thegraphene in the graphene suspension to the metal in the salt solution oralkali solution is 1:50-1:600.
 20. A liquid crystal display devicecomprising a conductive film, wherein the conductive film is formed ofthe conductive material according to claim 1.